Auto string merging in Python

Question

I have new string from file ("new.dat") to be merge with file ("old.dat").

File : "new.dat"
WBGG 120200Z VRB03KT 9000 FEW015 BKN160 28/25 Q1013 NOSIG

File : "old.dat"
WBGG 120130Z VRB02KT 9000 FEW015 BKN150 27/25 Q1013 NOSIG    
WBGG 120100Z VRB02KT 9999 FEW014 BKN150 26/25 Q1012 NOSIG

The expected output will overwrite and became new ("old.dat")

WBGG 120200Z VRB03KT 9000 FEW015 BKN160 28/25 Q1013 NOSIG
WBGG 120130Z VRB02KT 9000 FEW015 BKN150 27/25 Q1013 NOSIG    
WBGG 120100Z VRB02KT 9999 FEW014 BKN150 26/25 Q1012 NOSIG

The process will continue as the new string in "new.dat" appeared in the system. The result from the current script is weird. Anyone got ideas?

new=open("new.dat","r")
old=open("old.dat","r")

for line1 in new:
    data1=line1

for line2 in old:
    data2=line2   

newdata=np.array([data1,data2])

## overwrite file and become old file
newfile = open("old.dat", 'w')
newfile.write(newdata)
newfile.close()

If you are going to use np, you might aswell go for reading the files with np. Concatenate or vstack seems right way to go. — Anton vBR
– Anton vBR, Commented May 12, 2018 at 2:02
Please explain what is the "result from the current script" instead of just "weird". — user202729
– user202729, Commented May 12, 2018 at 2:05
I used python-2.7...the weird output is ignoring line no. 2. WBGG 120130Z....is missing.. — Azam
– Azam, Commented May 12, 2018 at 2:11

Anton vBR · Accepted Answer · 2018-05-12 02:24:13Z

1

This is what I meant with "sticking to numpy":

a = np.loadtxt('old.dat', dtype='object')
b = np.loadtxt('new.dat', dtype='object')

c = np.vstack((b,a))

np.savetxt('old.dat', c, delimiter=" ", fmt="%s")

Or you could use pandas:

import pandas as pd

(pd.concat((pd.read_csv(i, sep=' ', header=None) for i in ('new.dat', 'old.dat')))
    .to_csv('old.dat', sep=' ', index=False, header=None))

But I would probably use some shell script for this. Windows for instance (type this into terminal in the folder)

(type old.dat new.dat) >> old.dat

edited May 12, 2018 at 2:24

answered May 12, 2018 at 2:09

Anton vBR

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8 Comments

Azam Over a year ago

...it woroks..great. I am so happy for that...yess!!...but how to make sure the recent new data is place on top??

Anton vBR Over a year ago

@Azam You change the order of (a,b) to (b,a)

Azam Over a year ago

I did not know vstack is helpful in here...thanks again @Anton vBR

Azam Over a year ago

what if the data in different dimension or columns?. how to combine it..

Azam Over a year ago

the above example was in exact column hence no problem to use vstack...@Anton vBR

|

user2910787 · Accepted Answer · 2018-05-12 02:20:13Z

1

We can use append for writting new data to the old file ,as new data becomes old data for next incoming New data . Try to change

newfile = open("old.dat", 'w')

To

newfile = open("old.dat", 'a')

answered May 12, 2018 at 2:20

user2910787

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